Thank you for your question. Easily fitted to most undergravel systems and comes equipped with a tapered riser stem adapter, which accepts 1/2" to 1-1/8" tubing, adjustable flow control on all models except 110, filtered air intake, and an epoxy-filled motor. Models 20 and 30 feature a deflection shield for angled flow control, and Models 50 and 70 offer both forward and reverse water flow.

Thank you for your question. The outlet can be rotated approximately 270 degrees. The outlet catches on the housing on both sides. The filter will only fit the downward facing inlet.

I'm running mine at full capacity and the flow seems fine on my 75 gallon tank. It does have a flow control so you can adjust it as needed

Thank you for your question. The power head should be sized to your aquarium. Aquarium water should be approximately 5 times an hour. For a 50 gallon aquarium this would be 250 gallons per hour.

for a 120 gallon tank I would use the 70's. If they are too strong they have a flow control you can turn down to meet your needs.

yes you will be happy with 2 of them for 75 or 90 gallon. you can adjust flow but i have 2 on 75 gal and it really moves the water on full so i thin k it would also be enough for 90 gallon also.

Yes , also depending what size aquarium you have.

yes, the entire unit is completely submersible

For several years I have successfully used an old, (and still functioning quite nicely,) Aquaclear 30 power-head for doing exactly that. Returning water from a “bucket” to my tank while gravel cleaning. (Also while scraping algae off the tank walls.) As the Hagan Aquaclear power-heads have a venturi and are not rated for “foot of head.” The trick is both in the base (of the “Bucket”) elevation, and blocking off the venturi for this purpose. My early 1980's model 40L tank's top sits at an elevation of exactly four foot above the floor. (I have successfully been running this tank since the day I bought it new at the pet shop. Typically with Very Messy long-lived Goldfish and Otocinclus.) To use the Hagan Aquaclear 30 as a return pump: I have to elevate the bucket on a stool so that it's bottom is approximately 13 to 14 inches above the floor. The “bucket” I use is a modified 5 gallon hard walled plastic drinking water container (the kind used while camping,) with one side removed (cut out,) laying on its side. and a modified ¼ inch acrylic panel to hold a 50 micron filter sock. And a return hosing feed-through for a short length of hose which is coupled from the Hagan Aquaclear 30 power head. This makes the 'after gravel cleaning' part of the task easier. You do need to keep an eye on the level in the “Bucket” and take a short break once in a while to let the power head “catch up.” For the “Algae Scraping” in lieu of a Standard 'Gravel Scraper', I use an Algae Scraper I improvised myself, with the “scraper Head” made from ¼ inch acrylic, which is mounted on a handle which is a 12mm diameter by two foot length of 'Pyrex Glass' lab tubing, with fire polished ends. The Scraper head is mounted to this “handle” by the “melt through” method (And then Acrylic Solvent,) Specifically so that the “scraper tube handle” remains Uncapped. So that it can be coupled to the siphon hose. (Which is more typically that of a “Python clean and fill” in suction mode,) while scraping Algae and REMOVING it, (and its spores,) directly from the tank while scraping.

Yes, there is lever to change the water flow.